The present invention relates to electrical power switches and, more particularly, to electrical power switches including line-powered switching control means. More specifically, this invention relates to a remote controllable two-terminal AC electrical power switch including a line-powered switching control means. Yet more specifically, although not solely limiting thereto, this invention also relates to retro-fittable two-terminal wall-mountable power switch including line-powered remote-controllable switching control means. This invention also relates to circuit arrangements for switching on and off an electrical load by line-powered automated switching control means.
An electrical power switch is generally connected in series between a load and a power source in order to connect or disconnect (switch on or off) a load from an alternating current (AC) power source. When the switch is in the xe2x80x9cONxe2x80x9d state, a generally low impedance appears between the terminals of the switch and electrical power will flow from the power source, for example, the AC mains, to the load. On the other hand, when the switch is in the xe2x80x9cOFFxe2x80x9d state, a very high impedance will generally appear across the terminals of the switch, thereby preventing or blocking the flow of electrical energy from the power source to the load.
A conventional two-terminal power switch generally includes a conductive contact switching member which is pivotable or movable between an xe2x80x9cONxe2x80x9d and an xe2x80x9cOFFxe2x80x9d position corresponding respectively to the connection and or disconnection of the two terminals of the switch by the metallic conductive member.
Electronic switching devices such as power MOSFETS, transistors or thyristors are commonly used as switching means in electronic controlled electrical power switches since switching can be done without physically moving the conductive metallic member as in the case of conventional switches. However, the ON-state voltage drop across such devices is usually large and generates waste heat which causes heat dissipation problems, especially when the switch is enclosed in a small confined space, such as inside a wall socket.
Electro-mechanical switches such as relays which include a moveable conductive member connected to a magnetic core and coupled to a solenoid are also found in present day automated electrical power switches. However, conventional relay switches are usually bulky and require a continuous current to maintain a switching state. Such a continuous current causes heat dissipation problems as well as power supply problems. Electronic or electromechanical switching devices are particularly attractive nowadays because they can be used in soft-touch or automated switching schemes such as remote-control switching, motion-sensored or other detection-based power switching systems.
While soft-touch or automated switching schemes are generally preferred, such preferred switching schemes or devices generally require automated control and switching circuitry for controlling and/or effecting the actual switching. In addition, a power switch which is remotely controllable will provide great convenience to the public. However, such automated or remote controllable switching schemes generally require a power supply, usually a DC source but not necessarily limiting thereto, to operate the control and automated switching circuitry or the signal receivers.
For a three-wire AC wiring system, in which the live, neutral and earth terminals are available, the control or switching circuitry operating power may be obtained by connecting a power supply circuit between the xe2x80x9clivexe2x80x9d and the neutral or earth terminals. However, for a two-wire AC wiring system, in which the live or phase wire is connected through via a switching device, no neutral or earth terminals are available and the operating power supply may be obtained from an external power supply or directly from the AC power source. In the latter case, although the operating power may be obtained from the live wire alone or by additional wirings to the power source, this will usually involve additional wiring works which may be expensive and unsightly.
Obviously, it will be advantageous if the power supply to the control circuitry can be obtained directly from the live wire of the power source to which the switch is connected without requiring a separate power supply or additional wirings.
Where a power switch is used in location-fixed applications in a 2-wire environment, for example, for installation as a wall-mount power switch in a prewired wall socket, it may not be economical or practical to provide additional wirings to supply the necessary power. For such applications, an external power source will be inevitable unless the control and switching circuitry is line-powered. However, an external power supply usually means additional running costs as well as a more bulky and unsightly switching device.
Hence, it will be greatly advantageous if there can be provided switching devices or circuit arrangements in which the control or other peripheral circuitries can obtain their operating power from the live wire of the AC power source to which the switch is to be connected. However, since a power switch is usually connected in series with a load and between the two poles of an AC power source, the problems of getting line power to control switching are well known. In particular, a power switch is generally characterized by a high open-circuit voltage and a very low open-circuit leakage current when the switch is in the xe2x80x9cOFFxe2x80x9d state. At the same time, the switch is generally characterized by a low close-circuit voltage and a high close-circuit current across its two-terminals when the switch is on the xe2x80x9cONxe2x80x9d state. Because of these inherent characteristics, problems exist for supplying operating power to the controlling and switching circuitries during both the xe2x80x9cONxe2x80x9d and xe2x80x9cOFFxe2x80x9d state of a switch. Therefore, it will be advantageous if a two terminal power switch with line-powered switching and controlling circuitry (including remote-control circuitry) or circuit arrangements can be provided without undue complexity and in a sufficiently compact form.
In providing such line-powered circuitry or circuit arrangements, it will be highly advantageous if the additional on-state voltage drop across the terminals of the switch and the additional off-state leakage current due to the power supply to the control circuitry and the switching devices can be maintained to a minimum. A low off-state leaking current of less than 20 mA is generally required while a low on-state voltage drop is preferred since the product of the current and the voltage drop generally correlates to the power dissipation by the power switch itself.
In many conventional automated power switching circuitry, triacs or thyristors are usually utilized to facilitate electronic or non-contact power switching. Because of the inherent forward voltage drop of triacs or thyristors, power dissipation becomes significant and heat sinking requirements become critical. In higher current applications where a power switch is enclosed in a small and confined space during normal operation, for example, in a wall socket or cavity in case of a wall mounted power switch, triac or thyristor based switching devices may not be suitable due to the need of forced ventilation.
Hence, it will be of great advantage if there can be provided non-triac- or non-thyristor- based switching devices for use with the afore-described line-powered switching control circuitry to facilitate electronically controlled power switching while alleviating power dissipation problems associated with triac- or thyristor- based switching devices.
Furthermore, although electromechanical relay switches having a coil and a pair of normally open contacts have been proposed for use as switching devices in automated power switches, such relay switches have not been widely used in such power switches because a constant supply of DC current is generally required to maintain the mechanical conductive contacts in the closed positions. Such a DC current demand invariably means the need of a large current transformer in order to feed sufficient energy to the coil to maintain the closed positions. As a result, larger overall switch size as well as higher power dissipation become an issue. Therefore it will be desirable if improved switching devices can be proposed for use in automated power switches so that the demand of such DC current supply can be alleviated.
To enhance the applications or usefulness of the automated power switches and to improve user friendliness, it will be highly advantageous if such line-powered automated power switches can be controlled both locally or proximally at the physical location of the switch as well as remotely by, for example, radio-frequency or infrared control, motion, temperature, light or other sensor triggered switching schemes. In addition, the locally accessible control of such power switches usually includes a soft-touch toggle switching option so that only minimum physical effort is required for switching on or off the power switch. However, due to the somewhat effortless triggering of a soft-touch switch, the switch will be continuously and repeatedly turned on and turned off (xe2x80x9ctogglingxe2x80x9d) if the soft-touch button is kept pressed. This may be due to undesirable, mischievous or non-intentional switching such as prolonged pressing of the soft-touch button by a toddler or due to other un-intended false engagement of the switch. Hence, it will be highly desirable if the soft-touch control section is provided with means to neglect or discern such accidental, mischievous or un-intentional prolonged pressing of the soft-touch button.
In view of the afore-said, it will be beneficial for the public if electrical power switches with line-powered controlling and/or switching control circuitry which improve, alleviate or overcome shortcomings associated with switches of this type are provided. In light of the known problems associated with the open- and closed-circuit voltage and current characteristics of typical power switches, it will be greatly advantageous if there can be provided power switches with built-in power supply so that power for operating the control or switching circuitry and devices is available irrespective of the switching state of the switch.
Accordingly, it is an object of the present invention to provide AC electrical switches having line-powered switching control circuitry or circuit arrangements in which the switching device is generally non-triac or thyristor based. It is another object of the present invention that such line-powered automated electrical switches do not require a large DC current to maintain the switching device in its on- or off-states or to change the switching states. It is yet another object of this invention to provide a power switch in which the switching device is sufficiently compact, easy to actuate while providing adequate switching performance.
It is yet an other object of the present invention to provide electrical switches with line-powered control circuitry and xe2x80x9csoft-touchxe2x80x9d switching facility which is also provided with means to neglect mischievous or undesirable switching action such as prolonged pressing of the soft-touched button for local switching. It will be highly desirable if the afore-said objects can be implemented without compromising the benefit, safety and compactness of the power switches.
To provide additional convenience to the public, it is also an object of the present invention to provide power switches with line-powered controlling and switching circuitry which are remotely controllable. Preferably, such a remotely controllable power switch includes an option of being locally controllable at the physical location of the power switch.
It is also an additional object of the present invention to provide alternative circuit arrangements or topologies for use with line-powered controllable switches, whether in combination or separately, to alleviate problems with or to provide improvements to conventional switches.
As a minimum, it is an object of the present invention to provide the public with a choice of electrical power switches having line-powered control and/or switching circuitry or circuit arrangements for enhanced power switching control.
According to the present invention, there is provided an electrical power switch which includes:
a first and a second shunt circuit branches connected between said terminals,
a switching means in said fist shunt branch,
a control means for switching said switching means between a conductive xe2x80x9cONxe2x80x9d state and a substantially non-conductive xe2x80x9cOFFxe2x80x9d state,
a first and a second power supply circuits for supplying power to said control means respectively when said switching means is in the xe2x80x9cONxe2x80x9d or the xe2x80x9cOFFxe2x80x9d state,
said first power supply circuit includes a two-terminal circuit member which is connected in series with said switching means such that the same electric current will flow across both said switching means and said two-terminal member of said first power supply circuit,
said second power supply circuit is connected in said second circuit branch,
said control means includes means to generate electrical signals for switching said switching means to the xe2x80x9cONxe2x80x9d or xe2x80x9cOFFxe2x80x9d states.
According to the general scope of the present invention, there is provided an electrical power switch including a first terminal, a second terminal, a switching device connecting said first and said second terminals, switching control means for operating and controlling said switching device, and power supply circuitry connected to said first and said second terminals for supplying power to said switching control means, wherein said switching device includes a solenoid operated contact switching member, said contact switching member being movable between a circuit-closing position (the xe2x80x9cONxe2x80x9d position) and a circuit-opening position (the xe2x80x9cOFFxe2x80x9d position), said contact switching member remains in either said circuit-closing or said circuit-opening positions unless and until a switching current is sent through said solenoid to switch said contact switching member from said circuit-closing position (xe2x80x9cONxe2x80x9d position) to said circuit-opening (xe2x80x9cOFFxe2x80x9d) position or from said circuit-opening (xe2x80x9cOFFxe2x80x9d) position to said circuit-closing (xe2x80x9cONxe2x80x9d) position.
In general, said switching current to switch said contact switching member from said xe2x80x9cOFFxe2x80x9d position to said xe2x80x9cONxe2x80x9d position has a direction or polarity which is opposite to that for switching said contact switching member from said xe2x80x9cONxe2x80x9d position to said xe2x80x9cOFFxe2x80x9d position.
Preferably, said contact switching member is held in said xe2x80x9cONxe2x80x9d position by a magnetic core after a switching current of a first direction or polarity has been sent through said solenoid to magnetise said magnetic core.
Preferably, the energy required to switch said contact switching member from said xe2x80x9cONxe2x80x9d position to said xe2x80x9cOFFxe2x80x9d position is lesser than that required to switch said contact switching member from said xe2x80x9cOFFxe2x80x9d to said xe2x80x9cONxe2x80x9d position.
Preferably, said solenoid is connected to said switching control means via latching circuitry, said latching circuitry includes a first switched circuit branch connected to a first voltage source for switching xe2x80x9cONxe2x80x9d said switching device and a second switched circuit branch connected to a second voltage source, for switching off said switching device, the voltage of said first voltage source being higher than that of said second voltage source.
Preferably, said contact switching member is moved against spring urge when moving from said xe2x80x9cOFFxe2x80x9d position to said xe2x80x9cONxe2x80x9d position and said contact switching member moves with spring assistance when moving from said xe2x80x9cONxe2x80x9d position to said xe2x80x9cOFFxe2x80x9d position.
Preferably, said switching control means sends currents of opposition directions or polarities through said solenoid for switching on and off said switching device.
Preferably, said switching control means is connected to a signal receiver for receiving remote control signals, said signal receiver is operated by power obtained from said power supply circuitry.
Preferably, said switching control means is connected to a local control and a remote control receiver, said switching control means sends out signals to operate said switching device upon detection of switching demand signals from either said local control or said remote control.
Preferably, said switching control means is connected to at least a first and a second switching signal sensors which hare conjunctively connected, said switching control means sends out switching signals to operate said switching device upon detection of a switching demand signal from any of said sensors.
Preferably, said contact switching member is brought into the xe2x80x9cONxe2x80x9d position by magnetising a magnetic core which hold said contact switching member in its xe2x80x9cONxe2x80x9d position by the residual magnetic force in said magnetic core after the magnetising current has disappeared.
Preferably, said contact switching member is moved from said xe2x80x9cONxe2x80x9d position to said xe2x80x9cOFFxe2x80x9d position after a switching current of a direction or polarity opposite to said first direction or first polarity is sent through said solenoid in a direction to demagnetise said initially magnetised magnetic core.
Preferably, said first switched circuit branch of said latching circuitry includes a transistor with a common-collector connection and a transistor with a common emitter connection connecting to the two terminals of said solenoid.
Preferably, said switching demand signals include a signal with a variation of magnitude within a pre-determined period of time.